<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
小写转大写：{{ str1|upper }}<br>
大写转小写：{{ str2|lower }}<br>
切片操作：{{ slice_str|slice:"2:4" }}<br>
时间格式化：{{ time_str|date:"Y-m-d G:i:s" }}<br>
</body>
</html>